Large and medium-scale morpho-sedimentary features of the Messina Strait: insights on bottom-current controlled sedimentation and interaction with downslope processes

The Messina Strait is a ∼ 3-8 km wide and 40 km-long extensional area that connects the Tyrrhenian Sea with the Ionian Sea (Mediterranean Sea), and where tectonics, oceanographic and erosive-depositional downslope processes strongly interact each other. Based on the analysis of high-resolution multibeam data, we present an updated morpho-sedimentary framework that reveals a complex seabed morphology, characterized by a variety of features linked to bottom-currents and downslope processes. In particular, we recognize a suite of large to medium-scale erosive and depositional features, related to different bottom-currents (e.g., reverse tidal flows, residual flows, internal waves) acting over diverse time periods. Large scale bottom-current features are represented by contourite drifts and channels developed over long periods (> thousands of years). Medium-scale features formed during shorter time periods and include scours, furrows, transverse ridges (pinnacles) and narrow longitudinal bodies in the sill sector, along with several sand wave fields, located at greater depths on the Ionian and Tyrrhenian sides of the Messina Strait. Downslope processes encompass channelized features originated by sedimentary gravity flows, coarse-grained aprons and fans and submarine landslides. They mostly occur along strait margins and become predominant in the southern exit where the axial Messina canyon and its tributaries are present.Overall, our study shows that the MS is a fruitful area in which to investigate the interaction between recent erosive-depositional sedimentary and oceanographic processes, also modulated by sea-level fluctuations, during the last eustatic cycle. Moreover, the observed seabed morphologies and the associated processes provide insights for interpreting similar features in modern and ancient similar straits and seaways.

The Nazca Drift System – palaeoceanographic significance of a giant sleeping on the SE Pacific Ocean floor

The evolution and resulting morphology of a contourite drift system in the SE Pacific oceanic basin is investigated in detail using seismic imaging and an age-calibrated borehole section. The Nazca Drift System covers an area of 204 500 km2 and stands above the abyssal basins of Peru and Chile. The drift is spread along the Nazca Ridge in water depths between 2090 and 5330 m. The Nazca Drift System was drilled at Ocean Drilling Program Site 1237. This deep-water drift overlies faulted oceanic crust and onlaps associated volcanic highs. Its thickness ranges from 104 to 375 m. The seismic sheet facies observed are associated with bottom current processes. The main lithologies are pelagic carbonates reflecting the distal position relative to South America and water depth above the carbonate compensation depth during Oligocene time. The Nazca Drift System developed under the influence of bottom currents sourced from the Circumpolar Deep Water and Pacific Central Water, and is the largest yet identified abyssal drift system of the Pacific Ocean, ranking third in all abyssal contourite drift systems globally. Subduction since late Miocene time and the excess of sediments and water associated with the Nazca Drift System may have contributed to the Andean orogeny and associated metallogenesis. The Nazca Drift System records the evolution in interactions between deep-sea currents and the eastward motion of the Nazca Plate through erosive surfaces and sediment remobilization.

The Bottom Surface Sediment Transport Changes in Bathymetry in the Rupat Strait, Riau Province, Indonesia

The Rupat Strait is located at the eastern coast of Sumatera Island, Riau Province,Indonesia, under the influence of the current system flowing from the Malacca Strait into the Strait.The primary purpose of this study is to identify the topographyof Rupat Strait prevailed by bathymetry changes, which was analyzed using oceanographic and satellite images.This study was conducted in the Rupat Strait in July 2018 through two steps of research: 1) oceanographic observation; 2) bathymetry measurement.The study of oceanographic observation was carried out along the coastal areas of Dumai City and Rupat Island. The depth of Rupat Strait (bathymetry) was measured using an echosounder at 60 stations in July 2018. The changes in the depth of the Strait were analyzed by comparing data between depth in 1990 by satellite images and the depth in 2018 by the measurement. The results of study indicate that dominantly, the depth of the Strait has increased by 1.5-2.7 meters for 28 years. The depth of the Rupat Strait, based on the interpretation of the satellite image data of MIKE C-MAP (1990) ranges from 0.9 to 29.4 meters, and of the measurement in 2018, ranging from 2.4 to 32.1 meters.The dominant factor causing the changes are the current system flowing from the Malacca Strait through the Strait during high and low tides, and the surface bottom sediments are transported out the Strait by the current, including the bottom current.

Evolution of seafloor pockmarks along the Northern Orange Basin, Offshore South Africa: Interplay between fluid flow and bottom current activities

Pockmarks are pervasive geomorphologic features identified along continental margins resulting from fluid expulsion on the seafloor. However, the understanding of the underlying geological mechanism/control in relation to their evolution, distribution, and morphology is limited, especially along data-starved continental margins such as the Northern Orange Basin. Analysis of a high-quality 3D seismic reflection data reveals at least 50 individual pockmarks, two channel-like depressions and several irregular depressions in water depth ranging between 800 m and 2400 m. Morphologically, the pockmarks are circular, elongated, comet-like and crescentic in shape, with diameters and depths ranging between ∼0.2 - 2.8 km and ∼10 - 130 m, respectively. Preferential alignment of these pockmarks on the seafloor in relation to the axis of underlying turbidite channels, erosional morphologies and mass transport complexes portray a genetic relationship. The slope architecture hints at the possibility of both deep and shallow fluid source driving pockmark formation. Under this scenario, deep thermogenic gas derived from Cretaceous source rocks migrated along fault systems associated with the Late Cretaceous Megaslide complex to the overburden. The fluids are stored/redistributed in contourite and turbidite channels and subsequently focused toward the seafloor under an increased pore pressure regime. Yet, the fluids may be either solely biogenic gas or heterogeneous, incorporating biogenic components and pore-water derived from the channels and dewatering of the contourites. Importantly, the discovery of crescentic and elongated end-member pockmark morphologies indicate post-formation sculpting of the initial pockmark morphologies by bottom currents. The discovery of these deep-water pockmarks opens the possibility that such fluid escape features may be more widespread than currently documented in the Northern Orange Basin. This has implications in understanding of the petroleum system here and their potential role in the South Atlantic marine ecosystems and global climate change in terms of the expulsion of climate forcing gases.

Impact of Upward Oxygen Diffusion From the Oceanic Crust on the Magnetostratigraphy and Iron Biomineralization of East Pacific Ridge-Flank Sediments

Recent measurements of pore-water oxygen profiles in ridge flank sediments of the East Pacific Rise revealed an upward-directed diffusive oxygen flux from the hydrothermally active crust into the overlying sediment. This double-sided oxygenation from above and below results in a dual redox transition from an oxic sedimentary environment near the seabed through suboxic conditions at sediment mid-depth back to oxic conditions in the deeper basal sediment. The potential impact of this redox reversal on the paleo- and rock magnetic record was analyzed for three sediment cores from the Clarion-Clipperton-Zone (low-latitude eastern North Pacific). We found that the upward-directed crustal oxygen flux does not impede high quality reversal-based and relative paleointensity-refined magnetostratigraphic dating. Despite low and variable sedimentation rates of 0.1–0.8 cm/kyr, robust magnetostratigraphic core chronologies comprising the past 3.4 resp. 5.2 million years could be established. These age-models support previous findings of significant local sedimentation rate variations that are probably related to the bottom current interactions with the topographic roughness of the young ridge flanks. However, we observed some obvious paleomagnetic irregularities localized at the lower oxic/suboxic redox boundaries of the investigated sediments. When analyzing these apparently remagnetized sections in detail, we found no evidence of physical disturbance or chemical alteration. A sharp increase in single-domain magnetite concentration just below the present lower oxic/suboxic redox boundary suggests secondary magnetite biomineralization by microaerophilic magnetotactic bacteria living as a separate community in the lower, upward oxygenated part of the sediment column. We therefore postulate a two-phased post-depositional remanent magnetization of ridge flank sediments, first by a shallow and later by a deep-living community of magnetotactic bacteria. These findings are the first evidence of a second, deep population of probably inversely oriented magnetotactic bacteria residing in the inverse oxygen gradient zone of ridge flank sediments.

Sedimentary response to current and nutrient regime rearrangement in the Eastern Mediterranean Realm during the early to middle Miocene (southwestern Cyprus)

During the early and middle Miocene, the Mediterranean had become a restricted marginal marine sea with diminishing and ultimate loss of connectivity to the Indian Ocean. This dramatically changed the heat, energy, freshwater and nutrient budgets across the Mediterranean and most notably in its eastern basin. While one of the most prominent lines of evidence of this change in the Eastern Mediterranean is the onset of sapropel formation, many other aspects of the sedimentary system changed in response to this rearrangement. Here we present a detailed analysis of a hemipelagic succession from southeastern Cyprus dated to the late Aquitanian to the early Serravallian (22.5 – 14.5 Ma). This sequence is carbonate-dominated and formed during the decoupling of the Mediterranean Sea and the Indian Ocean. It exhibits sedimentation with mass transport contribution from shallow water carbonates to deeper facies with phosphatization and bottom current (at intermediate depth) interactions. This succession traces both local subsidence and loss of a local carbonate factory. Additionally, it records a shift in bottom current energy and seafloor ventilation, which are an expected outcome of connectivity loss with the Indian Ocean.

PREDICTING BOTTOM CURRENT DEPOSITION AND EROSION ON THE OCEAN FLOOR

Three types of oceanographic data are integrated in this study to predict thermohaline geostrophic bottom current deposition and erosion on the ocean floor. These data types are, 1) high-resolution bathymetry, 2) numerical model data of bottom current shear stress and 3) model data of the distribution and amount of sediment on the ocean floor. Intervals of thermohaline geostrophic bottom current deposition and erosion can be quantified from this information, which are then be extrapolated across the ocean floor in 4.5 x 9.3 km grid-size resolution. The results of this analysis are displayed on a map that shows the distribution of zones of bottom current erosion and deposition. This map is then cross-referenced for accuracy using documented examples of mapped erosional and depositional bottom current systems, which demonstrates this study’s approach has strong predictive capabilities. The model developed herein is used to derive boundaries for depositional bottom current regimes and formulate generalized patterns that contribute to bottom current erosion and deposition, and then discuss the importance of these interpretations for resource extraction and ocean floor mapping.